This invention relates to booster circuits such as booster circuits for boosting clock signals for charge pumps in programmable logic device integrated circuits, and more particularly, to booster circuits with capacitor protection circuitry.
Integrated circuits generally have a number of power pins and data pins. An integrated circuit's data pins are used to receive input signals from other integrated circuits and other signal sources. An integrated circuit's data pins are also used to provide output signals to components that are connected to the integrated circuit. Power pins are used to provide power supply voltages to an integrated circuit. In a typical digital integrated circuit, power pins may be used to receive a ground power supply voltage of 0 volts, a logic-level power supply voltage of 1.0 volts, and an elevated power supply voltage of 2.5 volts.
Circuit designers strive to use power pins efficiently. There is a reluctance to add power pins to an integrated circuit, even if a particular circuit design requires a power supply voltage that is not readily available from existing power supply pins. When extra power supply pins are added to an integrated circuit, the integrated circuit die must be made larger to accommodate the extra power supply pins or existing data pins must be converted to power supply pins. Increasing the size of the integrated circuit die can be expensive and can reduce device yields. At the same time, converting data pins to power pins is generally not desirable because this reduces the number of pins that are available for input and output operations and may require the integrated circuit to operate more slowly than would otherwise be necessary.
To avoid using additional power supply pins, circuit designers use on-chip voltage generation circuitry to generate new power supply voltages from the standard power supply voltages that are already available. If, as an example, a new power supply voltage of −0.5 volts is required, an on-chip voltage generator can be used to produce this voltage from standard ground and positive power supply voltages that are available from existing power supply pins. By generating the new power supply voltage using on-chip circuitry, it is not necessary to use an additional power supply pin to receive the new power supply voltage. System design tasks are also simplified, because it is not necessary to externally produce the new power supply voltage.
One popular type of on-chip voltage generator is based on charge-pump circuitry. Charge pumps contain a number of stages. The stages in a charge pump are driven by true and complementary versions of a clock signal. The size of the clock signal influences the efficiency of the charge pump. If a relatively low voltage clock signal is used, a charge pump may need to use a large number of stages to successfully produce its desired output voltage. If a relatively larger voltage clock signal is used, each stage of the charge pump will operate more effectively, so that fewer stages are required. By reducing the number of stages in the charge pump, circuit real estate consumption can be minimized.
A booster circuit can be used to increase the magnitude of a digital signal such as a charge pump clock. Booster circuits contain capacitors. With a conventional booster architecture, a thick-oxide capacitor is used that is able to withstand large voltages. Such thick-oxide capacitors exhibit a low capacitance per unit of surface area on an integrated circuit. As a result, conventional booster circuits consume large amounts of circuit real estate.
It would therefore be desirable to be able to produce booster circuits for boosting charge pump clock signals and other digital signals on integrated circuits such as programmable logic device integrated circuits.